Drainage control elements for paper machines



Nov. 14, 1967 J. H. PERRY DRAINAGE CONTROL ELEMENTS FOR PAPER MACHINESFiled April 7, 1966 2 Sheets-Sheet 1 INVENTOR /4ME5 z/PR) m E w \w 1 Rum Qw 9 6 m a 3659;;

Nov. 14,1967 JQ H. PERRY 3,352,749

DRAINAGE CONTROL ELEMENTS FOR PAPER MACHINES Filed April 7, 1966 2Sheets-Sheet 2 42 Tlcifi...

INVENTOR /4M s H. PEKRY United States Patent 3,352,749 DRAINAGE CONTROLELEMENTS FOR PAPER MACHINES James H. Perry, Worcester, Mass, assiguor toNorton Company, Worcester, Mass, a corporation of Massachusetts FiledApr. 7, 1966, Ser. No. 540,895 9 Claims. (Cl. 162-452) This applicationis a continuation-in-part of my copending application Ser. No. 203,086,filed June 18, 1962, now abandoned.

My invention, broadly speaking, is directed to the production of auniformly calipered paper web that is subsequently moved to the suctionboxes of a paper-making machine of the Fourdrinier type, to thepreservation of the original form of the straight-edge-ungrooved formingboards and foils for long time periods of use nothwithstanding thetendency of the wire to wear the wire contacting surfaces and edges ofthe forming boards and of the foils, and to the prolongation of wirelife.

As is well known in the production of the paper web in a Fourdriniermachine, the wood chips are processed to form pulp that is fed to theFourdrinier section of the machine. The pulp usually contains about 1percent wood fiber, 99 percent water and amounts of foreign materialsuch as abrasive grit, silicon, clay filler and many other foreignsubstances when it reaches the Fourdrinier wire.

This stock is forcefully projected at a relatively high velocity from ahead box which extends transversely of and substantially coextensivewith the width of the Fourdrinier screen. To project this stock onto thescreen at the breast roll, the outlet of the head box is provided with aslice, which is, in elfect, a transversely extending slot from which thestock issues. The adjustment of this slot controls the flow of the stockto the screen by regulating the velocity and amounts of stock issuingfrom the slot at various points in its length.

In actual practice in the industry, the stock is jetted through theslice from the head box to the screen at a greater speed than that ofthe screen.

Beneath the lower surface of the upper reach of the Fourdrinier screenbetween the breast roll and the couch roll are located a forming board,foils, suction boxes and table rolls.

The forming boards used commercially in the industry take several forms,two of which are illustrated in the drawings. The forward edge of theforming board, that is to say the edge adjacent the breast roll, isslightly spaced from the roll, making it possible for the portion of theupper reach of the Fourdrinier wire above the forming board to dipdownwardly into the said space as the upper reach of the Fourdrinierwire is drawn across the forming board under the weight of the stock orslurry. As the wire passes over the rear or trailing edge of the formingboard it will also dip.

The force required to pull the upper reach of the wire across theforming board will be increased by this dipping of the wire. The effectof this and of the weight of the slurry will subject the wire and thesurface and the edges of the forming board to a great amount of wear.

The result will be that the leading edge of the forming board as nowconstituted, adjacent the breast roll, will become worn and notched. Thewearing of the leading edge of the forming board results in the changingof its normally straight edge form into a transversely grooved ornotched form from which trough-like channels extend longitudinally ofthe machine in the upper surface of the forming board as a result of theprogressive wearing away of the face of the forming board. This wearpermits the slurry to be thicker (and thus contain more pulp) at thetrough-like locations than it is in between these locations across theface of the forming board. This uneven distribution of the slurry causesthe production of a web which is uneven in thickness or calipertransversely. A similar wearing of the trailing edge and the adjacentface portion of the forming board takes place as a result of the wiredipping over the trailing edge.

The wearing of the forward edge of the forming board and the formationof trough-like channels in the wire bearing face of the forming boardhas been a source of great concern not only because of replacement cost,but, importantly, because of the production of the uneven caliper of theweb and subsequently formed paper. Many efforts have been made toeliminate these undesirable conditions or to introduce means forcompensating for them, as, for example, so constructing the slice thatits output openings may be individually or in groups adjusted to feedmore or less pulp at given locations across the wire, as has alreadybeen pointed out.

As is well known in the industry, two distinct conditions prevail in theformation of Fourdrinier paper, one at the forming board location andthe other at the suction box locations. At the forming board, thesurface and leading and trailing edges of the board are subjected to thewearing action of the wires caused by the weight and velocity of thegreat mass of water, foreign material and pulp that are projected,jet-like, from the head box onto the wire, and to the change ofdirection of the wire from a straight line to an undulating line as itdips at the edges of the forming board and the edge of the foils.

On the other hand, when the web reaches the location of the suctionboxes, the slurry has been transformed into a self-sustaining web oforiented fibres, much of the water having already been extracted at theforming board, at the table rolls, and at the foils. Because the web ofpaper has already been formed by the time it reaches the suction boxes,the covers of the boxes are subjected to a relatively lesser downwardforce which is that created by the weight and speed of the upper reachof the Fourdrinier screen and the weight of the paper web and thesuction. The result is that the covers of the suction boxes aresubjected to less Wear and a different character of wear than are theforming boards.

Because the web is, in effect, a formed, self-sustaining paper stripcarrying less water than the water-carried mass of oriented fibres fromwhich it is formed, it is of lesser weight per unit area and thereforethe web has less tendency to dip over the edge of the suction box cover.The covers are, therefore, not subjected to the same destructiveconditions as are the forming boards.

My invention contemplates, particularly, the prolongation of the usefullife of forming boards so that they will resist the transformation oftheir straight edges into undulated or grooved edges and thetransformation of the upper surfaces from a plane into one which haslongitudinal channels that tend to produce a paper web of uneventhickness or caliper transversely.

It contemplates, also, the creation of forming boards that are of suchnature that, for long periods of time, the mat or partially formed webwhich passes from the forming boards over the foils and the table rolls,will be of substantially uniform thickness, the unit areas of which willbe of substantially the same density and will, in this condition, bepresented to the suction boxes.

It contemplates also the provision of suction box covers and foilsconstructed in such manner that they will not tend rapidly to wear thewire or to themselves become worn.

I have found that, in the preferred form of my invention, a greatlyimproved surface for forming boards and foils can be provided by makinguse of a hard, wearresistant refractory oxide material which, in someinstances is somewhat porous. Such a surface can be made service, becomefilled with water flowing from the pulp to form a lubricated surfacewhereby to minimize the friction between the moving wire and thestationery surface at certain locations.

In another form of my invention, the porous surface may be filled withan epoxy resin to provide an impervious surface. In both forms thesurface may be finished to have a very a smooth and substantiallyfriction-free characteristic. The coefficient of friction between thewire and such a surface is quite low, and excellent results are obtainedby providing such a surface on the above-mentioned forming board andfoils and other relatively fixed elements, such as suction box covers,of a Fourdrinier machine.

Preferably my invention contemplates an inert base such as a stainlesssteel or brass, etc. element which is coated with a nickel chrome alloylayer sprayed on the surface which faces toward the wire. An outersprayed metal oxide layer is then coated over the nickel chrome alloywith a flame spray means as taught in the Wheildon patent noted above.The metal oxide surface formed by this freezing of molten droplets insitu on the surface is somewhat porous and has a very hardwear-resistant characteristic. To obtain the proper finish it may beground and polished to have a high degree of surface smoothness tofurther minimize the possibility of wear resulting from the rubbingcontact against the under surface of the moving Wire.

In the drawings:

FIGURE 1 is a diagrammatic side elevation of a Fourdrinier wire sectionof a paper making machine showing, conventionally, some of the elementsassociated therewith;

FIGURE 2 is an enlarged diagrammatic side elevation of an associatedhead box, breast roll, forming board, and Fourdrinier wire;

FIGURE 3 is a fragmentary view showing a path of travel of theFourdrinier wire from the beast roll over the forming board and foils;

FIGURE 4 is a sectional view showing one form of a forming board;

FIGURE 5 is a sectional view showing a foil;

FIGURE 6 is a fragmentary sectional view showing one form of a suctionbox cover;

FIGURE 7 is a fragmentary sectional view of a modified form of foilstructure; and

FIGURE 8 is a sectional view showing a suction box.

At the head boxend of the Fourdrinier machine, the wire 10 is supportedon a free wheeling breast roller 11. The stock flows or is jetted ontothe generally horizontally directed upper run of the wire 10 justpastthe tangent point formed betwen the roller 11 :and the wire .as at 10A.At this point the wire has started on its paper-webforming generallyhorizontal run. As the wire leaves roll 11 with the stock flowing fromthe head box, the under surface of the wire is supported by a stationaryforming board 12.

A forming board structure used in the industry as shown in FIG. 4 maytake the form of a drain box 13 having a curved side wall 14 for closelyfollowing the curve of the periphery of roll 11..This forming board hasaflat upper bearing surface 15 which engages directly against theunderside of the wire, as the wire leaves the head box, to .preventwater from flowing too easily through the screen until fibers in thestock can get oriented thereon. The remaining portion of the uppersurface or top of the forming board has a series of slots formed in itthat permit water, whichthereafter drains through the wire, to flow fromthe underside of the wire into the box 13 for removal. The slots arefaced with lip elements16 which may, if desired, be curved and areconfigured to act as scraper means to remove the water droplets clingingto the underside of the wire. The action of the lip elements may bedesigned to retard or encourage water passage through the screen wherebyto assist in controlling the felting of the fibres as formation of thepaper bat progresses.

A series of table rolls 20 may be provided to carry the top run of thewire to near the end of the horizontal paper web or sheet forming run inso far as web is completed on the Fourdrinier wire..

The wire turns on the last of ther ollers 20 to angle downwardly to passaround the couch roll 22. The paper web leaves the wire just above thecouch roll for delivery to the first pair of press rolls and the wireturns around the couch roll to return to the head box end of its run bypassing over the set of support and tensioning rollers 23 and 24 androller 25. The couch roll is driven in the usual manner to provide thesole driving contact with the wire.

Between several of the table rollers 20 which engage the underside ofthe generally horizontal upper run of thewire, various relatively fixedelements may be disposed such as foils 30 and suction boxes 31. Enlargedfoil elements are shown in FIGS. 5 and 7. These foil elements serve as afurther scraper means which acts like the forming board 12 to controlthe removal of water draining through to the underside of the wire. Thefoil elements may have a drain box 32 for conveying the Water away fromthe wire but usually the water drains from the foil into the wire pit.The uppper surface of each foil is slotted so that the water can passfrom the underside of the wire into the box 32 or pit. Each slot has alip 33 for engaging against the underside of the screen to control waterflow through the screen and collect water from the underside thereof.The fiat surface 34 on the foil engages under the wire at the rear endof the foil and controls or slows the water flow through the Wire andsupports the wire on its travel toward the adjacent table roll 20 tolimit the wrap angle of the forming wire around this table roll 20. Thedeflector surface 34 may be independent of the foil elements and may bepositioned between table rolls 20 if desired. The foil element as shownin FIG. 7 has differently shaped scraper or lip elements 33 thereon forremoving the water from the underside of the screen in a manner suchthat no suction is produced by the configuration of the trailing edge.Some suction effect is inherent in the operation of the form of lip 33shown in FIG. 5.

Each suction box element 31, such as the one shown in more detail inFIG. 8 which receives the pre-formcd web of paper, includes a chest 35which is adapted to be evacuated and is therefore sealed on all sidesexcept the top. The suction box has perforated, slotted or otherpatterned openings in the top cover 36 for engaging against theunderside of the wire to suck water through the screen to aid incompletion of the pulp or paper web formation.

It is apparent that the very weight of the wire itself plus the addedweight of the stock carried on the wire and the effect of the jetting ofthe stock onto the wire cause the underside of the wire to have asignificant frictional contact with the relatively stationary surfacesof the forming board and the foils, especially where it engages theedges of the same. Even the engagement of the wire with the table rolls20 produces some frictional resistance and the interplay of all theforces encountered in driving and supporting the wire producesconditions that are not consistent with a long life for the wire screen,the forming boards, the foils and the suction box covers. Added to thisis the strain imposed on the wire by the heavy drag produced on the wirewhen the several elements engaging the underside thereof are operating.

Under ideal conditions a copper alloy wire being run on a conventionalhigh speed high production Fourdrinier machine such as is used fornewsprint paper, may operate for a relatively short period of continuousoperation. When conditions are not ideal and. a tear or unusual wearpattern develops such that a wire is destroyed in a shorter time,expenses mount up because not only must the expensive wire be discarded,but the entire paper-making plant is put out of operation until theFourdrinier machine can be fitted with a new wire. This entails loss ofproduction and the cost of the expensive skilled labor which must beused to handle the wire.

As I have pointed out, my invention is intended to provide an improvedsurface structure for those stationary element of such a machine whichengage the moving wire and I herein provide an improved construction forminimizing the wear of the forming boards, foils, suction box covers andwire elements and consequent down time whereby much more efficient papermaking results.

I accomplish my purpose by coating the wire bearing surfaces of suchelements as the forming board, the lips of the foils, and the suctionbox covers, as heretofore stated, with a hard, wear resistant refractoryoxide material. I have found that this not only incidentally prolongsthe life of these elements themselves more or less indefinitely but, inmy preferred form, this construction, also minimizes the frictionalengagement between these rubbing parts. While attaining theseadvantages, I have also found that the coating construction I specifydoes not permit gritty objects to lodge upon and become imbedded in asurface whereby another source of damage inherent in present dayFourdrinier structure is eliminated.

In following my preferred teaching the elements such as the formingboards and foils are covered with a hearing surface for minimizingfrictional engagement with the underside of the wire. These elements arepreferably formed as a base member of inert or corrosion resistantmaterials such a bronze or stainless steel which makes the best basemember for use in a paper making machine. The base member is preparedfor reception of the bearing coating of my invention by any suitablecleaning method, but I prefer to use a grit blasting procedure withabrasive grain such as fused aluminum oxide of about 16 to 24 mesh.

Insofar as my invention is applicable to suction box covers, aperforated stainless steel base member for a suction box cover 36 formedof 304 stainless steel is a typical structure to which my invention hasbeen applied and I have blasted it with aluminum oxide grit of 24 meshcarried in an air stream at a pressure of 40 pounds per square inch airpressure and sprayed at the rate of about to 30 square inches per minuteto condition the base member for the application of a flame-sprayednickel chrome metal undercoat 52 as shown in FIG. 6. The nickel chromealloy is composed of approximately 80% nickel and 2.0% chrome and may beapplied to the suction box cover by a conventional molten metal spraytechnique known as metallizing. A layer of nickel chrome approximately.003" thick will be found to be the optimum as an intermediate layer forreceiving the bearing layer 41 of my invention. A range in thickness,however, of from .002" to .006" has been found to be useful as anintermediate layer for the type of refractory metal oxide here describedand undercoatings as thick as .013 have been used. The forming boardsand foils may be similarly prepared.

The bearing layer I prefer is flame-sprayed onto the nickel chromeundercoat as taught in the Wheildon Patent 2,707,691 mentioned above.Any of the refractory oxides there disclosed will be found to be more orless satisfactory, but to date I have found chromium oxide to be bestfor my purposes. Alumina and zirconia silicate are 6 useful and in someinstances zirconia silicate, which has a particularly low coeflicient offriction for this purpose, is used.

The molten droplets of chromia or other refractory metal oxide aprayedonto the surface to be coated, freeze in situ upon landing on thesurface and flatten out as they solidify to form a rather laminated-likeporous coating. They form platelets in a layer preferably .040" thickthat interfit to lie generally in a plane parallel with the planesurface of the article being coated which structure produces a hard wearresistant coating that has an unexpected degree of flexibility. Thissurface layer may be from .010" to .070 thick. Such a surface formed ofchromia will have about 2% open and interconnected pores and a totalporosity of 4% and is extremely hard. While chromia is used to producemy preferred coating because of its hardness and ability to be finishedto take a high Polish, the alumina and zirconia or zirconia silicatecoatings, for example, may be more easly applied and have differentporosity characteristics. Alumina and zirconia silicate for example,have about 8% to 12% porosity with 4% of the porosity in the form ofopen and interconnected pores.

After deposition of my preferred coating, the chromium oxide surface isfinished to have a surface polish in the range of 7 to 30 RMSmicroinches and preferably I try to stay at the low end of the scale.This is accomplished by grinding the sprayed chromia layer with adiamond wheel and otherwise polishing the surface in a known manner suchas by lapping the final surface with fine grit diamond or boron carbide.A finish within this range is preferred to provide the best wiresupporting surface consistent with the porosity of the sprayed chromia,to trap droplets of water in the pores on the surface to form areservoir for liquid lubricant for the surface on which the wire rides.Such trapped water lubricates the wire as it moves over certain of thestationary surfaces to minimize friction, especially at the suction boxlocations, as has been pointed out.

In the instance of coating a suction box cover element, the perforationsthrough which the water from the Wire passes on its flow to the suctionbox must be ground and polished to produce a rounded shouldersurrounding the inlet to the perforation, as best seen in FIG. 6. Due tothe surface tension of the molten liquid deposited on the surface by thedescribed spray procedure, a somewhat rounded condition is inherentlyproduced as the coating solidifies. Nonetheless, I prefer to furtherpolish these corner surfaces to eliminate any and all sources ofpossible wear or damage to the wire. As more or less suction isintroduced in the several boxes 35, the flexible wire and the partiallyformed paper Web on its surface are caused to bow down somewhat into themouth of each of the perforations. If the corners or edges were notadequately rounded and polished, they would produce an undue wear on thewire by causing it to have a sharp bending action each time the wirepassed over the front and rear walls on each perforation in the suctionbox cover. The wear this bending action tends to produce on the wire canbe greatly minimized by providing a proper rounded configuration at thetop edges of the suction box openings. In the cases of forming boardsand foils, because of the wear producing factors heretofore pointed out,the smoothly rounded finish is produced on the leading edge of each ofthe lips of the forming boards and foil elements.

The coating of this invention has been found to be somewhat flexible andthis is important to the success of these elements of a Fourdriniermachine. For example, occasionally the wires vibrate and develop afluttering condition in use. The wear resistant characteristics togetherwith the significant flexibility thereof permit my coatings to continueto be operative under service conditions which have been found to beintolerable for more brittle substances. This property is also utilizedto overcome slight warpage and twisting thereof which may be expected infitting elongated elements such as foils, forming boards and suction boxcovers to existing Fourdrinier structures and of course is of incidentalvalue during,

shipping in commerce.

It may he sometimes happen that a portion of the coated surface made infollowing this invention will become worn unevenly in use. Thelaminated. surface structure I have described can be reground once orseveral times, depending upon the thickness of the final coating of therefractory metal oxide deposited on the base member. In other instancesthe coating may be damaged by a hard blow that will crack or spall alocalized area of the coating. Such a flaw can be remedied easily infollowing my teaching by simply removing all of the loose and damagecoating from that area and applying a new sprayed on surface to coverthat area only. After the localized area has been coated with a finallayer of refactory metal oxide to a depth slightly thicker than thedepth of the previous finish on the element, the patch may be grounddown and the surface refinished to blend in with the rest of thesurface. Also when the finished coating has been worn down so that itcannot be reground to fit it for further use, the Working surface can berebuilt on the base element. Since the coating procedure may be repeatedan idefinite number of times, it is obvious that the relativelyexpensive basev element coated and finished as I have taught, mayberecoated and finished in a relatively inexpensive manner and can be madeto last the life of the machine with which it is used.

As I have stated, the coated surface may in some instances be furthertreated by applying a resin thereto. Porous refractory metal oxidecoating which have been flamesprayed from a solid rod onto a surface,have beeen filled with either phenolic, epoxy or silicone resins, Theresins can be thinned and painted on the sprayed surface with a paintbrush and cured in a known manner. Resin penetration by capillary actionfills the open and interconnecting pores and by applying the resin inseveral applications, penetrations .030 deep have been attained inalumina coatings. A resin layer may be left to cover the entire surfaceof the coated element, but I prefer to polish the resin away so that therefractory metal oxide layer is exposed with the resin filling only thepores.

In FIGURE 3 of the drawing, which illustrates, conventionally, a headbox with the slice, a breast roll, a forming board and a section of theFourdrinier wire, a path of travel of the upper, reach of the wire isindicated. As the wire passes from the head box 42 to the adjacentbreast roll, such as at 11, it dips downwardly as at. 44 and must bedrawn upwardly to some degree over and in forceful contact with theleading edge of the forming board, as at 46. If the forming board is ofthe type that includesslots 48 the wire dips into the slots and will bedrawn over the leading and trailing edges of the forming board elements.

The continuous movement of the wire over the edges of the forming boardsand over their surfaces tends to wear the edges from straight form tobroken or notched form, as I have heretofore pointed out. The notchesacross the machine may be of different depths and different forms. Asthe Wire is drawn over these edges, sup

porting the weight of the pulp and the water and foreign material, thesenotches gradually extend over the surface of the forming boardlongitudinally of the machine forming channels or depressions withhigher lands intervening.

Recognizing the detrimental effect of these notches and channels, theindustry has attempted to overcome such effect by providing theadjustable slices. My invention is intended to counteract the cause atleast to the extent that the initial condition of the forming boards orfoils will be maintained for longer periods of time than was possiblebefore my invention.

In FIGURE 6 of the drawing I have shown the hard smooth and polishedceramic surfacing 50 on the undercoat 52 on the suction box cover andhave shown the edges of the suction boxes as protected by the ceramic at54.

In FIGURE 4 the ceramic facing 56 laps over the leading and trailingedges of the forming board element at 58 and 66. Thus the wearing of thewire contacting surfaces of the forming board will resist the wearing ofnotches and channels heretofore referred to with the result that forlong periods of time the mat that is formed by the draining off of thewater and the matting or felting of the fibres will be of reasonablyeven caliper transversely.

In FIGURES 5 and 7 this ceramic surfacing 62 is of the same general formas that on the forming board with its edge protecting portions.

Many modifications of my invention can be conceived. It is not alwaysessential that the undercoat layer 40 be used, but since this layerserves to more strongly adhere the refractory metal oxide layer to thebase element while simultaneously cooperating with the outer layer toform a somewhat more impervious composite layer, the undercoating with anickel chrome layer is used in my preferred construction. Where acompletely impervious coating is needed, as suggested above, thecompleted undercoat and metal oxide layering may be fully impregnatedwith an epoxy resin which fills into the pores to become integrated withthe coating applied to the base member. The epoxy resin sealsthe metaloxide layer by flowing into the open and interconnected pores and curingin place. The exposed surface may then be finished to have the desiredpolish to minimize wear and friction on the wire. All these and possiblyother modifications of this invention may occur to those skilled in theart which will fall Within the scope of the following claims.

What I claim is:

1. In a paper-making machine having a traveling screen for supportingwater-wet pulp during the drainage of water therefrom and transverselyextending plates arranged longitudinally and contacting said screen tocontrol the drainage of water from said pulp, the improvement whereinsaid plates have a smooth, hard, porous ceramic screen contacting faceportion.

2. In a paper-making machine having a traveling screen for supportingwater-wet pulp during the drainage of water therefrom and transverselyextending plates arranged longitudinally and contacting said screen tocontrol the drainage of Water from said pulp, the improvement whereinsaid plates have a smooth, hard, porous ceramic screen contacting faceportion and. a filler in certain of said pores.

3. In a paper-making machine having a traveling screen for supportingwater-wet pulp during the drainage of water. therefrom and transverselyextending plates arranged longitudinally and contacting said screen tocontrol the drainage of water from said pulp, the improvement whereinsaid plates have a smooth, hard, flexible screen contacting face portionof a ceramic, said face portion being sufliciently flexible to permitdistortion of the plate without substantial damage.

4. In a paper-making machine having a traveling screen for supportingwater-wet pulp during the drainage of water therefrom, and a foilarranged transversely thereof and contacting said screen to control thedrainange of water from said pulp, the improvement wherein said fill hasa smooth, hard, porous ceramic screen contacting face portion.

5. In a paper-making machine having a traveling screen for supportingwater-wet pulp during the drainage of water therefrom, and a suction boxcover arranged transversely thereof and contacting said screen tocontrol the drainage of water from said pulp, the improvement whereinsaid suction box cover has a smooth, hard, porous ceramic screencontacting face portion.

6. In a paper-making machine having a traveling screen for supportingwater-wet pulp during the drainage of water therefrom, and a formingboard arranged transversely thereof and contacting said screen tocontrol the drainage of water from said pulp, the improvement whereinsaid forming board has a smooth, hard, porous ceramic screen contactingface portion.

7. In a paper-making machine having a traveling screen for supportingWater-wet pulp during the drainage of Water therefrom and a foilextending transversely of and contacting said screen to control thedrainage of water from said pulp, the improvement wherein said foil hasa smooth, hard, porous ceramic screen contacting face portion, and afiller in certain of said pores.

8. In a paper-making machine having a traveling screen for supportingwater-wet pulp during the drainage of Water therefrom and a suction boxcover extending transversely of and contacting said screen to controlthe drainage of Water from said pulp, the improvement wherein saidsuction box cover has a smooth, hard, porous ceramic screen contactingface portion, and a filler in certain of said pores.

9. In a paper-making machine having a traveling screen for supportingwater-wet pulp during the drainage of Water therefrom and a formingboard extending transversely of and contacting said screen to controlthe drainage of Water from said pulp, the improvement wherein saidforming board has a smooth, hard porous ceramic screen contacting faceportion, and a filler in certain of said pores.

References Cited UNITED STATES PATENTS 3,006,782 10/1961 Wheildon 117463,067,816 12/ 1962 Gould 162374 OTHER REFERENCES Pye-Wear of FourdrinierWire Bearing Materials

1. IN A PAPER-MAKING MACHINE HAVING A TRAVELING SCREEN FOR SUPPORTINGWATER-WET PULP DURING THE DRAINAGE OF WATER THEREFROM AND TRANSVERSELYEXTENDING PLATES ARRANGED LONGITUDINALLY AND CONTACTING SAID SCREEN TOCONTROL THE DRAINAGE OF WATER FROM SAID PULP, THE IMPROVEMENT WHEREINSAID PLATES HAVE A SMOOTH, HARD, POROUS CERAMIC SCREEN CONTACTING FACEPORTION.